Lighting system for automobiles



E. c. BALLMAN.

LIGHTING SYSTEM FOR AUTOMOBILES.

APPLICATION FILED SEPT. 13, I915.

Patented May30, 1922.

Speed 16' Speed m In:

TATES PATENT OFFICE.

EDWIN .C. BALLMAN, OF ST. LOUIS, MISSOURI, ASSIGNUR TO VALLEY ELECTRIC COMPANY, OF WILMINGTON, DELAWARE. A CORPORATION OF DELAWARE,

' LIGHTING SYSTEFI FOR AUTOMOBILES.

To all whom it may concern:

Be it known that I, ED IN C. BALLMAN, a citizen of the United States, and residing at St. Louis, in the State of Missouri, have invented a certain new and useful Improvement inLighting Systems for Automobiles, of which the following is a specification.

This invention relates to a lighting system for automobiles and the like.

In the accompanying drawing, I Figure 1 designates a diagram illustrating the operation of an automobile lighting system in use at the present time;

Figure 2 is a diagram of a lighting system embodying this invention;

Figure 3 is a diagram similar to Figure 1, but illustrating the operation of'the system embodying this invention;

Figure l'is a diagram showing the relations of the currents in the different parts of the circuit; I

Figure 5 is a side elevation of the regulator; i I

Figure 6 is a section along the line 66, Figure 5; and,

Figure 7 is a section along the line 7-7, Figure 6.

In the lighting system now employed on automobiles, the lamps receive current from a low tension magneto. Now in a magneto, the field has a constant strength, so that the voltage, as well as the frequency, varies with the speed. As the speed of the magneto varies with the speed of the automobile, the voltage of the magneto,and therefore, the voltage at the lamp terminals, will increase with the speed, and the current, as well as the candle power,will,therefore-vary with the speed. This is shown in Figure 1, where the abscissa represents speed in miles per hour, while the ordinates represent voltage, frequency, current and candle power. It will thus be seen that the current passing through the lamp will be several times greater at maximum, or even at normal speed of, say twent miles an hour, than it will be at low speed, say ten miles an hour. If a low resistance lamp is used, it is liable to burn-out at high speed, while a high resistance lamp will be too dim at low speed; at any rate, the candle power of the lamps will fluctuate too much for satisfactory operation.

One of the objects of this invention, therefore, is to provide. an automobile lighting Specification of Letters Patent. Patgnted lu 30 1922 Application filed September 13, 1915.

Serial No. 50,408.

system, in which the current passing through the lamps will remain practically constant over the normal. range of speeds. I

Further objects will appear from the detail description, taken in connection with the accompanying drawings.

eferring now more particularly to Figure 2, 1O designates a magneto which is'of the low tension type.

Connected in circuit with the magneto armature is an incandescent lamp, and connected also in series with a lamp and the magneto, 1s a regulator, which is hereinafter more particularly described. The lamp is of the low resistance, low voltage, metallic filament, nitrogen filledtype. The regulator comprises a winding of low resistance and of high inductive reactance, having a mag-- netic core, whose reluctance, and therefore, whose permeability remains constant, irrespective of the generator speed, so that the coeflicient of-reactance or selfinduction of the reactanc'e winding remains practically constant at varying speeds of themagneto.

Now, as is well known, the current in any circuit, is equal to the impressed electromotive force divided by the impedance. This is usually expressed by the I following formula:

K/R +X The electromotive force is, of course, a function of the speed and may, therefore, be represented by SK, wheres represents the speed, and K a constant. Furthermore, the reactance X is also proportional to the speed, and may, therefore, be represented by SL, where L represents another constant, The above equation .(1) can, therefore, be written as follows:

If the resistance R is small. as compared to the reactance SL, then the above equation reduces to, p

which i itself a constant. i I i I Thismeans that in an alternating current circuit containing a low resistance and a high reactance, the current will, under certain conditions, be independent of the magneto speed; in other words, the current remains substantially constant for varying speeds of the magneto. This is, however. only true if the quantity L does not itself vary with the speed. The quantity L is really the coefficient of self-induction of the winding, and this is a function of the permeability of the magnetic circuit. )Vhere the magnetic circuit is a completely closed ferric circuit, then the reluctance and the permeability, and therefore, the quantity L will, of course, vary with the magneto speed. If, however, the magnetic circuit is made up of ferric and non-ferric parts, and if the re luctance of the non-ferric part is a large part of the total reluctance, then the reluctance of the magnetic circuit will remain substantially constant, and the quantity L will be practically constant for all speeds, or for at least for speeds over a considerable range.

There is, however, another factor which enters into the successful operation of such a system, and that is the resistance. In reducing equation (3) from equation (2), it is assumed that the resistance is so small as to be negligible. This is, of course, a necessary condition. A reactance whose core forms an open magnetic circuit has, however, so much magnetic leakage, that in order to obtain the proper high reactance, it is necessary to use many turns of wire. This, of course, means an increase in resistance of the reactance winding, which cannot be tolerated if the condition of equation shall be fulfilled.

In accordance with this invention, in addition to using a low resistance lamp, and a reactance winding, whose resistance is negligible, the core of this reactance is constructed to form a nearly closed magnetic circuit. This practically eliminates magnetic leakage, and therefore, permits the utmost minimum of wire to be used, in order to produce the required reactance. The reactance core is so proportioned that the nonferric part of the non-magnetic circuit, or the air gap, will represent about ninety-five (95%) per cent of the total reluctance. Since, of course, the reluctance of a ferric part of a magnetic circuit is'many times greater than the reluctance of air, on account of the great difference in permeability, it will be readily understood that even with a magnetic circuit, whose air gap will represent ninety-five (95%) per cent of the total reluctance, the air gap can be very small, so that the magnetic circuit will be a nearly closed one.

Referring now to Figures 5, 6 and 7, 15 designates a laminated core which has wound thereon a low resistance reactance winding 16, whose terminals are shown at 17. The core is preferably made of laminated sheets so as to reduce the eddy currents, and is perforated to receive fibre or ebonite pins 18, so that the winding and core may be mounted. in an iron shell .19, the coil and its core being positioned in this shell. as shown in Figure 7 by the ebonite pins, which provides a predetermined air gap. The shell is also grooved circumferentially as shown at 20, which grooves run parallel with the magnetic field in the shell, so as to reduce the eddy currents to a minimum. End caps 21, of brass or other nonferric material, close the ends of the shell, and these end caps have attaching lugs 22 so that the device may be attached in any suitable position on an automobile. An insulated bushing 23 i provided for the terminals.

The core parts of the regulator are so proportioned that the air gaps form about ninety-five (95%) per cent of the total rcluctance of the entire magnetic circuit. This can be proportioned initially, and can be adjusted very closely by slightly hammering the shell opposite the air gaps. until the right length air gaps are obtained, or by turning the coil or winding around in the shell, so that the inequalities of the shell will adjust the gap. After the proper air gap has been obtained, the shell can be filled with cement, so as to hold the parts firmly in position.

In accordance with this invention, therefore, there is connected in circuit with the magneto and the low resistance lamp, a reactance winding which, in order to satisfy the equations referred to above, has a low resistance and a high reactance, compared to the resistance of the lamp; the core of this reactance winding has a nearly closed magnetic circuit of constant reluctance, and of constant permeability, irrespective of the magneto speed; the system is, therefore, constructed and adapted to cause the reactance to vary directly with, and only in accordance with the speed and the frequency of the magneto, with the result that the voltage at the lamp remains substantially constant at varying speeds of the magneto.

In Figure 4 is represented the voltage relations, a representing the voltage at the terminals of the magneto, b the voltage at the terminals of the react-ance, and a the voltage at the terminals of the lamps. 0 represents the voltage at the terminals of the lamps when the voltage of the magneto has dropped the amount shown, and it will be seen how little effect a large drop in the voltage of the magneto has on the voltage at the lamps. The voltage at the lamp will, therefore, remain substantially constant at varying speeds of the magneto.

Figure 3 represents the actual conditions taken from an actual device. It will be seen that the difference in the current at five miles an hour and thirty miles an hour is only twenty per cent (20%), while the variation ten miles above normal or twenty milies an hour causes a'variation of only two an onehalf per cent (2%-%). It will, therefore, be seen that with this system, the current will remain substantially constant over the ordinary range.

The regulator itself is simple in construc tion, cheap to manufacture, and efiective in its operation, and, moreover, requires no adjustment during operation. It can be attached to any existing machine without requiring changing of parts.

It is obvious that various changes may be made in the details of construction, within the scope of the appended claims, without departing from the spirit of this invention. It is, therefore, to be understood that this invention is not to be limited to the specific construction shown and described.

Having thus described the invention, what is claimed is:

1. A lighting system for an automobile having a magneto, comprising, a low resistamp connected in circuit with said magneto, a winding of low resistance and of high reaotance connected in said circuit, and a core for said winding constructed to form a nearly closed magnetic circuit, adapted to cause the voltage at said lamp to remain substantially constant at varying speeds of said magneto, substantially as and for the purpose set forth.

2. A lighting ystem for an automobile having a magneto, comprising, a low resis- 3. A lighting system for an automobile having a low tension magneto, comprising,

a low resistance metallic filament lamp connected in circuit with said magneto, a regulating winding of low resistance and of high reaotance connected in said circuit, and a core for said winding having a combination ferric and non-ferric circuit proportioned so that its'reluctance remains substantially constant irrespective of the magneto speed so as to cause the reaotance of said winding to vary directly as and in accordance with the magneto speed, and the resistance and the reaotance of said circuit being so relatively proportioned, adapted to cause the voltage at said lamp to remain substantially constant at varying speeds of said magneto, substantially as and for the purpose set forth.

In testimony whereof I aihx my signature this 12th day of August, 1915.

EDWIN C. BALLMAN. 

